This invention relates to silver halide photographic materials containing novel couplers.
The recent improvement in the quality of image achievable with silver halide color photographic materials has been remarkable but not so in terms of their sharpness quality. One important means for providing improved sharpness is to reduce the thickness of the coating structure. Particularly in the case of a silver halide emulsion layer that is closer to the support of a multilayer coating, the optical path of the scattering of light incident on the surface of the light-sensitive material is long and it is largely for this reason that making that emulsion layer as thin as possible by reducing its binder content is held to be an effective means for providing improved sharpness. Conventionally known methods for reducing the thickness of emulsion layers are based on reducing the oil or gelatin content by using polymer couplers as taught in Unexamined Published Japanese Patent Application No. 28745/1984 or low-molecular weight couplers capable of efficient color formation as taught in Unexamined Published Japanese Patent Application No. 195234/1984. However, none of these techniques have been found to satisfy the need for efficient color formation or desilvering during processing. Unexamined Published Japanese Patent Application Nos. 200349/1987, 204257/1987 and 134454/1989 teach the use of couplers that have as a coupling-off group a dye whose maximum spectral absorption is shifted temporarily to shorter wavelength by blocking an auxochrome. Upon reaction with the oxidation product of a developing agent, such couplers form another molecule of dye in addition to the azomethine dye formed from ordinary couplers. These "one-equivalent couplers" are significantly improved in the efficiency of color formation over conventional couplers but the spectral absorption of the dye combined with these couplers is not shifted to sufficiently shorter wavelength so that the couplers per se will absorb visible light to cause unwanted phenomena such as desensitization.
Further, these couplers are colored and modes of their utility are limited. For example, they are not suitable for use in reversal films, color papers and other light-sensitive materials intended for direct viewing.